I love this thread!
I always like to buy Disney purses/totes/duffles/etc. each year. I wear them everywhere - I used them when I was in college, I take them around town, to the airports, to Disney (of course!), other trips, etc. I didn't find too many last August but I did find a cute leopard print one with hidden Mickeys in the pattern at the AK, on clearance too!
I love pins. I found the HM Stretching Room ones last year on my first trip to the Disney outlet! They were (I think) $2 or $3 each! I also love to buy them in the parks, trade with CMs and sometimes with nice guests at the pin tables. My favorites to find are Peter Pan (the character, but the movie too is great!), Jaq and Gus Gus, Haunted Mansion, real classics (Clarabelle, Horace, etc.) ... and any others that catch my eye, are part of collections, the Hidden Mickey ones, etc.!
I like buying tops or t-shirts but the ones for women are usually made of such thin material. I would love to find some with thick material and really unique designs (like resort specific, attraction specific).
Then there are some of the best things of all - the confetti from the parades, the brochures, napkins, shopping bags ... they remind me of my trips most of all!